The invention relates to a process for the ex-situ presulfuration of a catalyst for the hydroconversion of hydrocarbons in the presence of hydrogen and of at least one sulfurated compound.
Catalysts for the hydroconversion of hydrocarbons and particularly for the hydro-treatment of petroleum cuts generally contain at least one element of group VIII or group VI of the periodic classification or a combination of several elements from these same groups, deposited on an amorphous oxide support, for example zeolithic such as for example the designated solids .CoMo/Al2O3, NiMo/Al2O3 or NiW/Al2O3. To enable the catalysts to be active for different hydrotreatment reactions, i.e. hydrodesulfuration, hydrodenitrogenization, demetallation or demetallization and certain types of hydrogenation, it is desirable to carry out a sulfuration of the metals with the aim of creating an active phase of the mixed sulfur type. This pre-conditioning stage must be carried out with the greatest care as it conditions the future activity of the product in its subsequent use. It can be carried out according to two different methods. The conventional technique, called in-situ sulfuration, consists of carrying out this pretreatment after loading the catalyst into the hydrocarbons conversion reactor.
The other method of activating this type of catalyst is to carry out an ex-situ sulfuration, i.e. outside the hydrotreatment reactor as described in various patents of the Assignee, for example U.S. Pat. Nos. 4,719,195, 5,139,983, 5,397,756, EP-A 785022.
The object of the present invention is to carry out an ex-situ presulfuration of the catalyst in the presence of hydrogen and at least one sulfarated compound which can be sulfurated hydrogen or any other compound containing sulfur. The invention is characterized in that, with the aim of improving the sulfuration or presulfaration, the catalyst is brought into contact with at least one hydrocarbon compound. This hydrocarbon compound is added either preferably at a stage before the presulfuration stage, or also before and during the said presulfuration stage.
Thus, the catalyst is preferably brought into contact with the hydrocarbon compound during a stage before the presulfuration stage. In this case, the hydrocarbon compound can be deposited using any method, for example using the method of dry impregnation of the catalyst by the hydrocarbon compound. This impregnation takes place cold, i.e. at normal temperature. It will most often be enough to introduce the hydrocarbon compound into the porosity of the catalyst at least superficially. It is not necessary to go xe2x80x9cto pore volumexe2x80x9d. Thus, the pore volume of the catalyst is filled completely or at least in part. Preferably, during this treatment, 10 to 100% of the total pore volume of the catalyst is impregnated for example, and more particularly 30 to 100%, by the said hydrocarbon compound.
The said hydrocarbon compound is chosen from the group constituted by the liquid hydrocarbons, but more particularly the compounds containing oxygen, and particularly alcohols, acids, ketones, aldehydes and other compounds containing oxygen. Vegetable oils, nitrogenous compounds, sulfurated compounds, polysulphides (in particular organic), and more particularly also oil bases or base lube oil, for example 150 Neutral (150 N) type, diesel oils and possibly white spirits can also be used. The latter have already been used in earlier catalyst presulfuration procedures, but they were used as vector solvents of sulfurated compounds with which the catalysts (in particular organic polysulfurs) were presulfurated, whereas here the catalyst is firstly impregnated in its porosity with these white spirits.
The sulfuration phase can be carried out at atmospheric pressure in a rotary system heated to between approx. 200 and 500xc2x0 C. In the case of a gaseous hydrogen/sulfurated hydrogen mixture, the partial sulfurated hydrogen pressures can vary within the range of 0.05 to 0.7. The introduction of the reagents can be carried out at the point of injection of the initial solid or at the point of ejection of the final solid, the sulfuration is thus respectively called co-current sulfuration or counter current sulfuration.
A possible explanation of the benefit brought about by sulfuration in the presence of a carbon compound consists of a thermal effect. The reactions transforming these oxide phases into sulfur phases are very exothermic. If this production of heat is poorly controlled, it can lead to significant heatings of the catalyst bed which, apart from the obvious problems of the safety of the process, can lead to the formation of poorly dispersed sulfur phases. This fritt of the active phase would lead to mediocre catalytic properties. One of the means of improving the control of the temperature at the time of sulfaration consists of impregnating the oxide catalyst with a hydrocarbon compound preferably before the sulfuration stage proper. This addition probably acts as a heat store during the exothermic sulfuration stage and permits an appreciable diminution of the increase in temperature, in particular in the core of the particle. The choice of this hydrocarbon compound will be made from the wide range of organic compounds containing or not containing a functional group.
Another possible explanation of the benefit brought about by this invention can be the following: the mechanism of the sulfuration of an oxide phase like the mixture of MoO3/CoO or NiO oxides supported on alumina involves a complete recomposition and a migration of species to the surface of the support. The structures of the initial and final phases are fully described in the literature. The oxide phase is comprised of well dispersed species at the surface of the alumina such as polymolybdates or tungstates associated with cobalt or nickel oxides. The active phase is structurally very different from this oxide phase. It is in the form of polygonal sheets of molybdenum or tungsten sulfur, generally stacked in a small number from 1 to 5 for conventional preparations, with cobalt or nickel atoms, so-called promoters, being situated on the periphery of these sheets. It is assumed that the catalytic activity is a function of the fine structure of this mixed phase and more precisely of the location of these border atoms, be this in an edge or corner position of these often hexagonal sheets. It is possible to imagine that the necessary migration of species can be influenced by the presence or not of hydrocarbon species on the surface of the solid, thus slightly modifying the structure of the mixed phase. Another hypothesis which can be proposed is that the carbon itself can be part of the active phase and thus directly modify the catalytic properties. This role of the carbon would obviously be different from that, better known, of depositing coke during the product utilization cycle, provoking the progressive reduction in catalyst performance values.
The entire disclosure of all applications, patents and publications, cited above and below, and of corresponding French application 98/12.739, filed Oct. 12, 1998, are hereby incorporated by reference.